1. Field of the Invention
The present invention is related to a step-up power supply circuit for producing a higher step-up voltage than a preselected power supply voltage, and also to an integrated circuit device equipped with the step-up power supply circuit.
2. Description of the Related Art
Conventionally, in an electronic appliance with employment of a dry cell and an on-vehicle battery, having relatively low output voltages, a step-up power supply circuit is provided. The step-up power supply circuit produces a step-up voltage in response to the output voltage of the above-described power supply. This step-up voltage is used as an operating power supply voltage in this electronic appliance.
FIG. 8 represents an example of an electronic appliance arranged by employing the above-described conventional step-up power supply circuit 1 and a semiconductor integrated circuit device 2 having a plurality of amplifiers AM.sub.0 to AM.sub.3. In this drawing, the step-up power supply circuit 1 is equipped with a rectangular wave generating circuit 4 and a step-up circuit 5, which are operated under a power supply voltage Vcc outputted from a power supply 3 such as a dry cell and an on-vehicle battery.
The rectangular wave generating circuit 4 is constituted by an astable multivibrator and the like, which outputs such a rectangular wave Sc. The amplitude of this rectangular wave is rapidly inverted in a predetermined time period. The step-up circuit 5 is arranged by a voltage doubler rectifying circuit equipped with a rectifying diode and a capacitor. The step-up circuit 5 ON/OFF-controls the rectifying diode in synchronism with the rectangular wave Sc to charge the capacitor, so that a step-up voltage HVcc higher than the power supply voltage Vcc is produced.
This step-up voltage HVcc is applied to the semiconductor integrated circuit device 2, and since the amplifiers AM.sub.0 to AM.sub.3 are operated while using the step-up voltage HVcc as the operating power supply voltage, these amplifiers AM.sub.0 to AM.sub.3 amplify signals entered into input terminals IN.sub.0 to IN.sub.3 to thereby output the amplified signals to the respective output terminals Q.sub.0 to Q.sub.3.
As previously explained, in the electronic appliance, the step-up power supply circuit 1 for producing the higher step-up voltage HVcc than the power supply voltage Vcc of the power supply 3, and the amplifiers AM.sub.0 to AM.sub.3 are operated under the operating power supply voltage HVcc, so that the dynamic range may be extended.
On the other hand, in the above-described conventional step-up power supply circuit 1, since the rectifying diode contained in the step-up circuit 5 is ON/OFF-controlled based upon the rectangular wave Sc containing the radio frequency (high frequency) components, the RF (radio frequency) switching noise is produced from the rectifying diode. There is a problem that this RF switching noise is entered into the amplifiers AM.sub.0 to AM.sub.3 provided in the semiconductor integrated circuit device 2 and then is mixed with the respective amplified signals derived from the output terminals Q.sub.0 to Q.sub.3.
As the conventional problem avoiding means, the step-up power supply circuit 1 and the semiconductor integrated circuit device 2 are separately mounted on the electric circuit board. Also, the ground GND1 of the step-up power supply circuit 1 and the ground GND2 of the semiconductor integrated circuit device 2 are formed on the electric circuit board in such a manner that these grounds GND1 and GND2 are separated from each other. Furthermore, the capacitors, resistors, coils and the like capable of absorbing the above-described RF switching noise are mounted on the electric circuit board.
However, there is another problem that since such a problem avoiding means is conducted, a total number of electronic components is increased and the entire electric circuit board becomes bulky. Also, both the step-up power supply circuit 1 and the semiconductor integrated circuit device 2 are separately arranged in order to prevent the adverse influence caused by the above-explained switching noise. As a result, while the total quantity of electronic components are increased, the high-performance electronic appliance can be hardly realized within a limited volume in high density.